The present invention relates to a method of expanding a tubular element in a borehole formed in an earth formation.
In the technology of borehole drilling for the exploitation of hydrocarbon fluids, the borehole is generally provided with a casing or liner to prevent collapse of the borehole wall. It has already been tried to apply radially expandable casings or liners, whereby the casing/liner is lowered into the borehole and thereafter radially expanded by pulling an expander through the casing/liner. One of the advantages of such procedure is that there is no longer a need for the conventional nested arrangement of borehole casings of stepwise decreasing diameter. However it has appeared that the pulling force necessary to pull the expander through the casing/liner can be prohibitively high.
It is an object of the invention to provide an improved method of expanding a tubular element in a borehole formed in an earth formation, whereby the pulling forces needed to pull an expander through the tubular element are reduced.
In accordance with the invention there is provided a method of expanding a tubular element in a borehole formed in an earth formation, the method comprising:
installing the tubular element at a selected location in the borehole;
installing a pulling string in the borehole, the pulling string extending in longitudinal direction through the tubular element and having an upper part connected to a pulling device at surface and a lower part provided with an expander of outer diameter larger than the inner diameter of the tubular element, the expander being arranged below at least part of the tubular element to be expanded, the upper part being connected to the lower part by a connector allowing rotation of the upper part relative to the lower part about the longitudinal axis of the pulling string; and
pulling the expander through said at least part of the tubular element by operating the pulling device so as to pull the pulling string in upward direction, and simultaneously rotating the upper part of the pulling string relative to the lower part thereof.
By simultaneously pulling the string and rotating the upper part of the string it is achieved that the longitudinal component of friction between the string and the borehole wall or tubular element, is significantly reduced or even eliminated. Consequently the pulling force no longer needs to counteract said longitudinal friction component.